Carbohydrate Loading for Sustained Physical Exertion

Some athletes add extra carbohydrates to their diets. This practice, called carbohydrate loading, increases the amount of glycogen stored in muscles. This carb-loading diet is not for everyday use, nor will it help people competing in events of short duration. It’s strictly for events lasting longer than 90 minutes.

Here’s how carb loading works:

The small amount of glucose in your blood and cells provides the energy you need for your body’s daily activities. The 400 grams of glycogen stored in your liver and muscles provides enough energy for ordinary bursts of extra activity.

But what happens when you have to work harder or longer than that? For example, what if you’re a long-distance athlete, which means that you use up your available supply of glucose before you finish your competition? (That’s why marathoners often run out of gas — a phenomenon called hitting the wall — at 20 miles, six miles short of the finish line.)

If you were stuck on an ice floe or lost in the woods for a month or so, after your body exhausts its supply of glucose, including the glucose stored in glycogen, it starts pulling energy first out of fat and then out of muscle. But extracting energy from body fat requires large amounts of oxygen — which is likely to be in short supply when your body has run, swum, or cycled 20 miles. So athletes have to find another way to leap the wall. Here it is: They load up on carbohydrates in advance.

You start about a week before the event, exercising to exhaustion so your body pulls as much glycogen as possible out of your muscles. Then, for three days, you eat foods high in fat and protein and low in carbohydrates to keep your glycogen level from rising again.

Three days before the big day, reverse the pattern. Now you want to build and conserve glycogen stores. What you need is a diet that’s about 70 percent carbohydrates, providing 6 to 10 grams of carbohydrates for every kilogram (2.2 pounds) of body weight for men and women alike. And not just any carbohydrates, mind you. What you want are the complex carbohydrates in starchy foods like pasta and potatoes, rather than the simple ones more prominent in sugary foods like fruit. And of course, candy.

What about while you’re running, swimming, or cycling? Will consuming simple sugars during the race give you extra short-term bursts of energy? Yes. Sugar is rapidly converted to glycogen and carried to the muscles. But you don’t want straight sugar(candy, honey) because it’s hydrophilic (hydro = water; philic = loving), which means that it pulls water from body tissues into your intestinal tract.

Using straight sugar can increase dehydration and make you nauseated. Thus, getting the sugar you want from sweetened athletic drinks, which provide fluids along with the energy, is best. The label on the athletic drink also tells you the liquid contains salt (sodium chloride). Why? To replace the salt that you lose when perspiring heavily.